French authorities are bracing for the arrival of an oil slick that is creeping toward its southwest coast and should make landfall on Sunday or Monday.

The 10-kilometer (six-mile) by one-kilometer oil sheet was first spotted by a French naval aircraft on Wednesday afternoon, after a fire aboard an Italian Grimaldi Lines container ship that capsized and sank Tuesday 300 kilometers west of the town of La Rochelle. The oil slick could reach the coast of southern Brittany by the end of the weekend.


This photo provided on Thursday March 14, 2019 by the Marine Nationale, shows the Grimaldi vessel Grande America on fire in the Bay of Biscay, off the west coast of France, Monday March 11, 2019. (Loic Bernardin/Marine Nationale via AP)

In addition to 2,200 tons of heavy fuel the "Grande America" had onboard, it was also transporting 2,000 cars and 365 shipping containers, 45 of which held dangerous materials, including a hundred tons of hydrochloric acid and 70 tons of sulphuric acid.

"There is a risk, so we must do everything to reduce it and to reduce the impact of pollution of our coasts," Environment Minister Francois de Rugy told BFM news channel.

Operations would be difficult due to high winds and heavy seas, with waves of 4 to 6 meters, de Rugy said, adding that in the conditions it was unlikely floating barriers could be deployed to hem in the slick.

Submarines could also later be deployed to check for cracks in the hull of the ship, which sank in 4,600 meters of water some 333 kilometers off the French coast after a fire.

The 214-meter long ship was sailing from Hamburg, Germany, to Casablanca, Morocco, when a fire broke out on Sunday.

Britain's Royal Navy frigate Argyll rescued all 27 crew members from the water.

Forecasts show fragments of the slick reaching parts of the Atlantic coast by Sunday or Monday.

French authorities aim to limit the impact of the spill by deploying four ships and preparing for a cleanup operation on land. They have also requested assistance from the European Maritime Safety Agency (EMSA) and have ordered the ship's operator to take action to prevent pollution.

"[This shipwreck] is problematic," said Christian Buchet, director of the Centre of Ocean Studies at the Catholic Institute of Paris, in an interview with RTL.

"Everything that burned -- the containers, the drums of hydrochloric and sulphuric acid -- that doesn't disappear. It goes up into the atmosphere."

The cause of the fire is unknown, but it is believed to have broken out on the car deck before spreading to a container, according to Jean-Louis Lozier, head of the regional maritime authority.

"Dilution in the ocean would not have serious consequences for the environment," Lozier said.

He added that the pollution risk posed by the chemicals "would be very localized."

But not everyone agrees.

"The major threat for the ocean is acidification," explained Buchet. "The ocean absorbs our pollution and it is dying because of it."

The French environmental campaign group Robin des Bois (Robin Hood) said it intended to file a criminal complaint over the environmental damage.

"Two thousand vehicles -- it's a car crash at the bottom of the sea, representing hundreds of tons of toxic materials in an area very rich in fish, plankton and marine animals," said the NGO's spokesman Jacky Bonnemains, adding he also feared coastal pollution.

Local authorities have opened an investigation.

But Yannick Jadot, a French member of the European Parliament and environmental activist, believes that not enough has been done to prevent such disasters.

"It's tragic, the laxity that often exists regarding maritime transport," Jadot said, adding that the oil slick would be "tragic for the French coast".

The last spill off the French coast occurred in December 2011, when the cargo ship TK Bremen ran aground in northwest France, losing an estimated 70 tons of fuel.